This invention relates to electrodynamic transducers, and primarily to the construction of moving coil loudspeakers. However, it is believed useful in other applications as well.
Various configurations of centering spiders for loudspeakers are known. There are, for example, the centering spiders illustrated and described in U. S. Pat.: Nos.2,201,059; 2,295,483; and, 5,715,324. This listing is not intended as a representation that a thorough search of the prior art has been conducted or that no more pertinent art than that listed above exists, and no such representation should be inferred.
Loudspeaker suspensions include a diaphragm surround and a voice coil centering spider. The function of the spider is to keep the voice coil centered in the loudspeaker""s permanent magnet motor air gap, while at the same time permitting linear motion of the voice coil in the air gap, and thus driving the diaphragm, to which the voice coil is mounted by the coil former, in as linear a fashion as possible. Ordinarily spiders are constructed from thermosetting resin-impregnated woven materials, such as natural and synthetic fibers. The resin-impregnated material is then heated in a mold to form corrugations, or rolls, usually concentric with the axis of the voice coil former, and usually of equal height and equal radius. The spider is then attached at its inner perimeter to the coil former and at its outer perimeter to the loudspeaker magnet motor assembly or loudspeaker frame, usually where the frame and motor assembly are joined to each other. The inner perimeter of the spider thus undergoes the same excursion as the coil former, and the outer perimeter of the spider is stationary, being mounted to the frame and/or motor assembly.
Conventional spiders exhibit asymmetric stiffness with respect to force versus deflection. When calculating the volume of material in the rolls of a conventional spider, it is clear that there is more material in the outer rolls, that is, in the rolls at increased distances from the axis of the coil former. Due to this increased amount of material in the rolls at greater distances from the axis of the coil former, the stiffness of the rolls varies regressively outwardly. That is, stiffness decreases with increasing distance from the axis of the voice coil and coil former.
According to the invention, a transducer includes a supporting frame, a motor assembly providing a magnetic field across an air gap, a coil former supporting a voice coil in the magnetic field, a diaphragm attached to the coil former and coupled by a surround at its outer perimeter to the frame, and a spider having an inner perimeter coupled to the coil former and an outer perimeter coupled to at least one of the frame and motor assembly. The spider includes a plurality of rolls. The roll next adjacent the inner perimeter has a first height. The roll next adjacent the outer perimeter has a second height less than the first height.
Illustratively according to the invention, the transducer further includes at least one intermediate roll having a third height less than the first height and greater than the second height.
Further illustratively according to the invention, the height of the rolls decreases linearly from the roll next adjacent the inner perimeter to the roll next adjacent the outer perimeter.